Tuning arrangement



C. W. PARK TUNING' ARRANGEMENT Filed April 19, 1957 Ww ...M -MM I i -aar/ur INVENTOR Y /qM/w/ ATTORNEY Patented Apr. 4, 1939 UNITED STATES PATENT OFFIQE TUNING ARRANGEMENT Delaware Application April 19, 1937, Serial No. 137,623

Claims.

This invention relates to tuned circuits, and particularly to such of these which are known as resonant lines.

As is now known, a resonant line is a tuned circuit comprising a pair of parallel conductors having substantially uniformly distributed inductance and capacitance. The line may consist oi inner and outer concentric conductors or a pair of straight linear rods coupled together at one or more points in their lengths. Such resonant lines may be used as the frequency controlling element in an electron discharge device oscillator, or as an input or output circuit of an amplifier, or as a ilter. Examples of concentric lines and the forms they may take are described in the article by Clarence W. Hansell entitled Resonant lines for frequency control, published August, 1935, in Electrical Engineering, pages 852 to 857, to which reference is made for a more detailed description.

Heretofore, in tuning or changing the resonant frequency of the resonant line, it has been customary to change the physical length of the line, as is described, for example, in the Hansell article, supra. The present invention simpliiies the tuning procedure, and provides a novel and simple means for effecting the tuning of the resonant line.

Essentially, the invention consists in the use of a rotatable short-circuited metal ring of low resistance placed in the magnetic field about the resonant line for changing the inductance of the tuned circuit. Rotation of the ring causes a change in the number of magnetic lines which are cut by the ring, with a consequent change in the tuning of the system.

A better understanding of the invention may be had by referring to the following description which is accompanied by a drawing, wherein Figs. 1, 2 and 3 illustrate differently arranged resonant lines equipped with the present improvement, together with an associated electric discharge device circuit given by way of example only. Fig. 4 illustrates a ring of rectangular form for tuning the resonant line.

Fig. l shows a tuned circuit in the form of a concentric resonant line comprising an outer conductor I and an inner conductor 2 conductively coupled together at one or" their adjacent ends by means of an end plate 3. The resonant frequency of the line is determined by such factors as the length of the inner conductor 2 of the line, and the ratio of diameters of the inner and outer conductors. For effecting a changein the resonant frequency of the line, there is provided, in accordance with the invention, a short-circuited metallic ring of low resistance 4, placed, as shown, between the conductors and in the magnetic ileld of the line. Ring 4 is rotatable in position by means of knob 5, which is located externally of the line and connected to the ring by a screw or metallic rod 6. The ring 4, it will be noted, is not in contact with the conductors I, 2, and is located at a point of substantial maximum current flow in the resonant line. In the position shown in the drawing, ring 4 will cut a maximum number of magnetic lines produced by the current in the two conductors I, 2 and will thus lower the inductance of the line circuit; the lowered inductance, in turn causing the tuned circuit to operate at a higher frequency. When ring 4 is rotated 90 from the position indicated, a minimum number of magnetic lines will be cut and the line will then operate at its nearly resonant frequency. Intermediate frequencies are dependent upon the intermediate angles the ring makes with respect to the conductors of the line.

Although screw 6 is shown as being a metallic connection, it should be understood that the ring can be mounted on an insulating rod or support. A metallic connection to the line, however, such as by means of screw 6, may be employed where the point of connection is at the same potential as the two conductors of the line, in the manner shown in the drawing. It will be'understood, of course, that the ring may be supported at the side from a rod extending through the outer conductor of the line, instead of from the end plate 3.

Furthermore, although ring 6 is illustrated as being located at a point of substantially maximum current flow, the ring can take other positions along the line, but the tuning band will decrease as the ring is moved from the point of maximum current towards the extremities of the line.

The line I, 2 is here shown connected by way of example only, as the frequency controlling element in the input circuit of an electron discharge device oscillator 'I whose output is coupled to any suitable utilization circuit 8, Electron discharge device 'I consists of a grid 9 which is coupled to the inner conductor 2 of the resonant line over a path including a grid-leak I, a cathode II, and an anode I2, the latter of which is connected' to a parallel tuned output circuit i3. Since the operation of the electron discharge device oscillator forms no part of the present invention per se, and is not necessary for an understanding thereof, it will not be further described herein.

Fig. 2 illustrates the ring I applied to a U- shaped concentric resonant line consisting of inner conductors I" and outer conductors 2', 2". The short circuited ring functions to change the frequency of this line in identically the same way described above in connection with Fig. 1. U-shaped line I', 21, I", 2 is here shown used as thefrequency controlling element of a pushpull type of oscillator comprising electron discharge devices I4 and I5 whose grids I 6 and II,

respectively, are coupled to suitably spaced points on the inner conductors. Where a greater range of tuning is desired, several additional rotatable rings 4', 4 located at places where the current density is highest and insulatingly supported at the sides by means of insulating rods 6', 6', as shown, may be employed. These additional rings 4', 4 not only give individual control of the two lines, to some extent, but can be used to compensate for the individual input impedances of the vacuum tubes I4 and I5 that will be used for replacements.

In Fig. 3, the short oircuited ring 4 is shown coupled to a resonant line consisting of two straight, linear rods I 8 and I9 which are conductively connected together by a base plate 20. Here again, the resonant line is used to stabilize the frequency of a push-pull oscillator having a pair of electron discharge devices 2|, 22. In this figure the grids of the devices are coupled to points along the lengths of the conductors.

In one embodiment of the invention, using a resonant line of the type shown in Fig. 3, with a push-pull oscillator having type ITX-245 vacuum tubes, the frequency of the tuned circuit was changed from a resonant frequency of 57 megacycles with the short circuited ring at minimum position to a frequency of 57.5 megacycles. The length of the resonant line was 47.5 inches, the diameter of each rod 2.0 inches, and the center to center spacing 4 inches.

Although the short circuited ring of the invention has been shown as being circular in form, it will be apparent that the ring may be rectangular, or take other forms without departing from the spirit and scope of the invention. Fig. 4 illustrates a rectangular ring which has the advantage over other forms of rings of giving a tighter coupling between the line conductors and the ring. Consequently, it is. to be distinctly understood that the term ring as used in the specification and appended claims is intended to designate any electrically closed or short-circuited path of low resistance without limitation as to a particular form.

Moreover, although the ring has been shown and described as being spaced from the conductors of the line, in order not to make physical contact therewith (except perhaps at the point of support in accordance with the principles outlined above), the tuning of the line can also be accomplished when the ring does make contact with the line in one of its positions. However, in such a case, the contact between the sides of the ring and the conductors of the line would be equivalent to any metallic connection between the conductors, and the resonant line would not function at its maximum efliciency, since the full utilization of the line depends vupon the low resistance of the circuits.

What is claimed is:

1. A resonant circuit comprising a pair of conductors having substantially uniformly distributed inductance and capacitance and so coupled as to form a tuned circuit, means for tuning said resonant circuit comprising an electrically closed path of low resistance placed in the magnetic field of said circuit, said path being rotat able through an arc for changing the resonant frequency of said line.

2. A resonant line comprising a pair of'spaoed parallel conductors coupled together to form a tuned circuit, and means for tuning said line comprising an electrically closed path of low resistance located between said conductors in such manner as to cut the magnetic lines of force set up by said conductors, said path being rotatable through an arc for changing the resonant frequency of said line.

3. A resonant line comprising a pair of spaced parallel conductors coupled together more closely at one of their adjacent ends than at their other end, an electrically closed path of low resistance placed in the magnetic field set up by said line for changing the resonant frequency of the line, and means for changing the angular position of said electrically closed path with respect to said conductors.

4. A resonant line comprising a pair of spaced parallel conductors coupled together more closely at one of their adjacent ends than at their other end, and means for tuning said line comprising an electrically closed path placed in the magnetic field set up by said line at a pointof substantially maximum current flow therein.

5. A resonant line comprising an inner and an outer concentric conductor conductively coupled together at one of their adjacent ends, a metallic closed ring positioned between said conductors near said one end, and means for changing the angular position of said ring with respect to said conductors for changing the resonant frequency of said line.

6. A resonant line comprising inner and outer concentric conductors, a metallic plate connecting said conductors together at one end, a metallic electrically closed ring of low resistance and of substantially circular form located between said conductors. near said one end, said ring being mounted on said plate, and means located externally of said conductors for rotating said ring, whereby the resonant frequency of said line may be changed.

'7. A resonant line comprising a pair of parallel electrically conductive rods coupled together more closely at one of their adjacent ends than at their other end, and means for tuning said line comprising a metallic electrically closed ring positioned between said rods near said one end, said ring having means for changing its angular position with respect to said rods.

8. A resonant line comprising a` pair of spaced parallel conductors coupled together more closely at one of their` adjacent ends than at their other end, and means for tuning said line comprising an electrically closed, rotatable, rectangular ring placed in the magnetic i-leld set up by said line at a point of substantially maximum current ow therein.

9. A resonant line comprising an inner oonductor and a surrounding outer conductor arranged in the form of a U, and means individual to each leg of said U for tuning same, said means consisting of an electrically closed, rotatable ring of low resistance positioned between the inner and outer conductors at a point of high current density.

10. A tuned circuit comprising a pair of coaxially arranged outer and inner surfaces of revolution so constructed and arranged. as to form an oscillatory circuit, and means for tuning said circuit comprising an electrically closed rotatable path of low resistance located between said surfaces of revolution.

CHARLES W. PARK. 

